The key assumptions used in the fair value less costs of disposal calculation are oil and natural gas prices (see Note 1), production volumes and the
discount rate (see Note 1). The sensitivity of the headroom to changes in the key assumptions was estimated. Due to the non-linear relationship of
different variables, the calculations were performed using a number of simplifying assumptions, including assuming a change to the variable being
tested only, therefore a detailed calculation at any given price may produce a different result.
It is estimated that if the oil price assumption for all future years was approximately 15% below the current assumption for 2020 and beyond, this
would cause the recoverable amount to be equal to the carrying amount of goodwill and related non-current assets of the segment. It is estimated that
there is no reasonably possible change in the price assumption for natural gas that would cause the recoverable amount to be equal to the carrying
amount of goodwill and related non-current assets of the segment.